Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$26.88	6.728%	$28.6885	$28.69	$28.70	$28.70
Purchase #2	$223.84	4.275%	$233.4092	$233.41	$233.40	$233.40
Purchase #3	$151.87	13.239%	$171.9761	$171.98	$172.00	$172.00
Purchase #4	$144.98	4.267%	$151.1663	$151.17	$151.15	$151.20
Purchase #5	$182.67	6.845%	$195.1738	$195.17	$195.15	$195.20
Purchase #6	$149.43	13.402%	$169.4566	$169.46	$169.45	$169.50
Purchase #7	$171.85	5.541%	$181.3722	$181.37	$181.35	$181.40
7 purchase totals =	$1,051.52		$1,131.2427	$1,131.25	$1,131.20	$1,131.40